executing init and fini

Question

I just read about init and fini sections in ELF files and gave it a try:

#include 
int main(){
  puts(\"main\");
  return 0;
}

void init(){
  put         


        

Answer 1

It is not a bug in ld but in the glibc startup code for the main executable. For shared objects the function set by the -init option is called.

---

This is the commit to ld adding the options -init and -fini.

---

The _init function of the program isn't called from file glibc-2.21/elf/dl-init.c:58 by the DT_INIT entry by the dynamic linker, but called from __libc_csu_init in file glibc-2.21/csu/elf-init.c:83 by the main executable.

That is, the function pointer in DT_INIT of the program is ignored by the startup.

If you compile with -static, fini isn't called, too.

DT_INIT and DT_FINI should definitely not be used, because they are old-style, see line 255.

The following works:

#include 

static void preinit(int argc, char **argv, char **envp) {
    puts(__FUNCTION__);
}

static void init(int argc, char **argv, char **envp) {
    puts(__FUNCTION__);
}

static void fini(void) {
    puts(__FUNCTION__);
}


__attribute__((section(".preinit_array"), used)) static typeof(preinit) *preinit_p = preinit;
__attribute__((section(".init_array"), used)) static typeof(init) *init_p = init;
__attribute__((section(".fini_array"), used)) static typeof(fini) *fini_p = fini;

int main(void) {
    puts(__FUNCTION__);
    return 0;
}

$ gcc -Wall a.c
$ ./a.out
preinit
init
main
fini
$